Spanning a number of years, many U.S. patents have issued to one Constant Johan Nauta of Overveen, Netherlands relating to single screw and multiple screw mixers. U.S. Pat. No. 3,109,633 Nauta may be representative of a single screw mixer while U.S. Pat. No. 3,450,390 Nauta may be representative of a multiple screw mixer. Although these patents are of interest, it should be noted that no search of the U.S. patent art has been conducted with reference to the specific invention shown, described and claimed herein.
Generally, in multiple screw mixers the driving connection at the upper end of the screw and the outer end of the orbit arm is such as to support the screw, the lower end of the screw simply being received in a suitable guide means on a support arm which rotates along with the orbit arm. In a representative single screw mixer, however, the screw is actually supported at its lower end, rather than just guided, the connection at the upper end of the screw to the outer end of the orbit arm being such as to not only drive the screw but also to permit a certain amount of flex to accommodate screw distortions which may be occasioned by the forces encountered during mixing. It is necessary, therefore, to positively support the lower end of the screw and this is wherein the improvements of this invention reside.
In addition to the single point contact disclosed in the U.S. Pat. No. 3,109,632 Nauta, three other bottom supports have been utilized. One of these has comprised a universal joint in effect connecting the screw at its lower end to the bottom of the truncated, inverted cone comprising the single screw mixer. The universal joint connects the screw to a support shaft in such manner that the screw and support shaft rotate together at screw speed which may in the neighborhood of 30 to 120 rpms; additionally the joint must accommodate the orbit arm speed of another 1 to 4 rpms. This universal joint is thus subjected to much wear and is expensive to manufacture and maintain; furthermore, it may also be contaminated by the product being mixed. Another arrangement involved the use of a ball like configuration on the lower end of the screw, such configuration being received within a bearing provided with a mating cover whereby to achieve what has been termed a captive ball support. Again, however, the arrangement connecting the lower end of the screw to the lower end of the mixer involves a bearing surface which must accommodate parts moving at the relatively high screw speeds encountered. This relatively high screw speed, along with the load which the bearing surface must support, necessitates that the bearing surface be made of specially hardened steel and involves the use of difficult and expensive manufacturing techniques.
Yet another manner of supporting the lower end of the screw has been to provide a pintle in the lower end of the mixer and a block in the lower end of the screw configured to ride on the rounded upper end of the pintle. Even with this arrangement, however, the bearing requirements above mentioned must be met. And the possibility of contamination earlier mentioned is also a factor with these latter arrangements as well.
It is believed that the present invention fully overcomes the kinds of problems encountered by the prior art and briefly reviewed above.